Radiant heater with improved radiating bars and mounting means therefor

ABSTRACT

A radiant heater which includes a housing and radiating bars fitted into the housing with their radiating surfaces expose outwardly. Hinged end caps close the end of the housing and have flanges which overlie the ends of the radiating bars to hold the bars in place. The radiating bars are further positioned by a plurality of cross struts which traverse the interior of the housing and have retaining ears thereon which engage the sides of the bars to laterally position the bars. The retaining ears on the center cross strut moreover interlock with adjacent tabs on the bars to further prevent the bars from bowing outwardly at the center of the housing. The tabs exist only at the retaining ears of the center cross strut so that the bars may be shifted longitudinally a short distance and then withdrawn from the housing when the end caps are open. Each bar includes a metal case having a center portion on which the radiating surface for the bar exists and edge portions which double back behind the center portion to form inwardly opening grooves. An electrical heating element extends along the back side of the concave portion and is captured in the grooves formed by the edge portions of the case. A strip of high temperature dielectric material is interposed between the heating element and the metal case. When the heating element is energized, it heats the metal case and causes the same to radiate heat from its center radiating surface.

tlnited States Patent [191 Desloge 1 RADIANT HEATER WITH TMPROVED RADIATING BARS AND MOUNTING MEANS THEREFOR [75] Inventor: George B. Desloge, Frontenac, Mo.

[73] Assignee: Watlow Electric Manufacturing Company, St. Louis, Mo.

[22] Filed: July 117, 1972 [21] Appl. No.: 272,385

219/553 [51] int. Cl. 1105b 3/06 [58] Field of Search 219/339, 345, 347,

[56] References Cited UNITED STATES PATENTS 1,013,157 l/19l2 Hadaway, Jr. 338/287 X 1,015,923 1/1912 Actmeyer.... 219/228 1,477,602 12/1923 Simon 51/135 2,795,685 6/1957 Browne 219/536 X 3,510,940 5/1970 Orr 29/611 2,254,068 8/1941 Frank 174/117 FX 2,857,499 10/1958 Fearn 219/536 X 2,882,376 4/1959 Charbonneau.. 219/536 X 2,976,387 3/1961 Browne 219/536 X 3,141,089 7/1964 Hultgreen 219/352 3,684,859 8/1972 Desloge 219/354 Primary Examiner-Velodymyr Mayewsky Att0rneyEdward A. Boeschenstein et a1.

57 ABSTRACT A radiant heater which includes a housing and radiating bars fitted into the housing with their radiating surfaces expose outwardly. Hinged end caps close the end of the housing and have flanges which overlie the ends of the radiating bars to hold the bars in place. The radiating bars are further positioned by a plurality of cross struts which traverse the interior of the housing and have retaining ears thereon which engage the sides of the bars to laterally position the bars. The retaining ears on the center cross strut moreover interlock with adjacent tabs on the bars to further prevent the bars from bowing outwardly at the center of the housing. The tabs exist only at the retaining ears of the center cross strut so that the bars may be shifted longitudinally a short distance and then withdrawn from the housing when the end caps are open. Each bar includes a metal case having a center portion on which the radiating surface for the bar exists and edge portions which double back behind the center portion to form inwardly opening grooves. An electrical heating element extends along the back side of the concave portion and is captured in the grooves formed by the edge portions of the case. A strip of high temperature dielectric material is interposed between the heating element and the metal case. When the heating element is energized, it heats the metal case and causes the same to radiate heat from its center radiating surface.

112 Claims, 6 Drawing Figures PATENTEDUBT 2m '3'.7s3.349

- SHEET 10F 2 PATENTEDUBT 2 1 sum 2 (1F. 2

RADIANT HEATER WITH IMPROVED RADIATING BARS AND MOUNTING MEANS THEREFOR BACKGROUND OF THE INVENTION This invention relates in general to heaters and more particularly to electric radiant heaters. It represents an improvement over and contains subject matter in common with the radiant heater disclosed in the co-pending application of George Desloge, Ser. No. 112,743, filed Feb. 4, I971, now US. Pat. No. 3,684,859.

Most radiant heaters of current manufacture contain ceramic components and have reflectors to properly distribute the heat. The ceramic components tend to crack easily and cannot withstand prolonged cycling of the heating elements. The reflectors, on the other hand, discolor easily. As a result, the efficiency of these heaters decreases and the output varies after a short period of operation. Moreover, most heaters of current manufacture, are not easily serviced, and this is particularly true of the heating elements.

SUMMARY OF THE INVENTION A principal object of the present invention is to provide an electric radiant heater which is extremely durable and can withstand prolonged cycling. Another object is to provide a heater of the type stated which is easily manufactured from inexpensive materials. An additional object is to provide a radiating bar which is formed in a simple rolling operation with no welding. A further object is to provide a radiant heater having no glass or ceramic parts. An additional object is to provide a radiant heater of the type stated which is compact and light in weight. Still another object is to provide a radiating bar which heats uniformly over its radiating surface, reaches its operating temperature rapidly, and has better electrical characteristics because the surface leakage path is increased.

The present invention is embodied in a radiating bar provided with metal case having a central'radiating portion behind which an electrical heating element is disposed. The heating element is captured in inwardly opening grooves formed in the bar. The invention also resides in a radiant heater having a housing provided with a positioning member which serves to position the radiating bars. Both the bars and the positioning member have interlocking restraining elements to prevent the bars from moving outwardly. The invention is further embodied in a housing having end caps which are locked in the closed position by resiliently mounted locking projections. These and other objects and advantages will become apparent hereinafter.

DETAILED DESCRIPTION OF THE DRAWINGS In the accompanying drawings which form part of the specification and wherein like numerals and letters refer to like parts wherever they occur:

FIG. I is a perspective view of a heater constructed in accordance with and embodying the present invention, the heater being partially broken away and in section; k

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1 and showing one of the end caps in its open position and further showing one of the radiating bars partially broken away and in section;

FIG. 3 is a sectional view taken along lines 33 of FIG. 2;

FIG. 4 is a'fragmentary sectional view taken along lines 4-4 of FIG. 1;

FIG. 5 is a perspective view of a radiating bar forming part of the present invention; and

FIG. 6 is a sectional view taken along lines 6-6 of FIG. 5.

DETAILED DESCRIPTION Referring now to the drawings, H designates a radiant heater which basically includes a housing 2, a plurality of radiating bars 4 positioned side-by-side in the housing 2 and exposed outwardly from one side thereof, and a block 6 of insulating material contained within the housing 2 behind the radiating bars 4.

The housing 2 includes (FIGS. 1-3) a channelshaped base member II) which is preferably formed from stainless steel sheet and consists of a pair of parallel sidewalls I2 and a back wall 14 formed integral with and interconnecting the sidewalls I2. Outwardly from the back wall 14 the two sidewalls ll2 are turned inwardly and doubled back a short distance upon themselves to form curved rims 116 (FIG. 3) through which reinforcing rods 18 extend. The rods 18 project beyond the ends of the rims 16 to form short locking projections 20 (FIG. 4), the ends of which are rounded off. The rods 19 are spot welded to their respective rims 16 only at one point and that point is located inwardly from the locking projections 20 to provide the rods 19 with some flexibility.

The housing 2 further includes a pair of end caps 24 (FIGS. I and 2) which are formed from a heat resistant metal such as stainless steel or so-called aluminized steel which is a steel having an aluminum coating thereon. The end caps 24 normally close the ends of the channel-shaped base member 10, but may be swung to an open position to expose the interior of te member 10 and the ends of the radiating bars 4. Each end cap 24 has an end wall 26 which extends across the end of the channel-shaped member 10 and closes the same, as well as a pair of side flanges 28 and a single cross flange 30 interconnecting the side flange 28. The side flanges 28 normally overlie the sidewalls 12 of the channelshaped member 10, whereas the cross flange 30 overlies the rims 16 of the sidewalls 12, as wellas the ends of the radiating bars 4. Thus, the cross flanges 30 serve to retain the bars 4 in the housing 2. The end wall 26 and side flanges of each end cap 24 project beyond the base wall 14 of the channel-shaped member 10 to form a mount for the heater H. i

In addition each end cap 24 is provided with an electrical insulating material 31 against the portion of its end wall 26 which is exposed to the interior of the housing. The material should be capable of withstanding high temperatures. Mica is ideally suited for this purpose. 4

Each end cap 24 is secured to the channel-shaped base member 10 by a hinge 32 (FIG. 2), the individual leaves of which are spot welded to the end wall 26 of the fonner and the back wall 14 of the latter. The hinges 32 allow the end caps 24 to fold outwardly away from the ends of the channel-shaped member 10 to expose the interior of the housing 2 and the ,ends of the radiating bars 4 therein. Each end cap 24 at the corners therein formed by the junctures of its end wall 26 and its side and cross flanges 28 and 30 is apertured to receive the locking projections 20 on the reinforcing rods 18 (FIG. 4). Since the rods 18 are welded to the rims 16 at only one point and are therefore somewhat flexible, the locking projections 20 will retract as the flanges 28 and 30 of the end caps 24 pass over them. Once the locking projections snap into the apertures at the corners of the end caps 24, the end caps are locked in their closed positions. To fold the end caps 24 outwardly, the locking projections 20 engaged with them must be depressed through the apertures sufficiently to clear the side and cross flanges 28 and 30. Alternatively, the end caps 24 may be locked in their closed positions by screws extended through the side flanges 28 thereof and threaded into the sidewalls 12 of the base member 10, all as illustrated in US. Pat. No. 3,684,859. Indeed, the end caps may be secured exclusively by a plurality of such screws, in which case the hinges 32 would not be necessary.

Spanning the two sidewalls 12 of the channel-shaped member I are cross struts 40 (FIGS. 1 and 3), the out wardly presented surfaces of which serve as positioning surfaces for the radiating bars 4. The cross struts 40 are positioned near the ends of the base member as well as at or near the center thereof. While three cross struts 40 are illustrated more may be utilized. For example, instead of having one cross strut 40 at the exact center of the base member 10, two may be utilized with one on each side of the exact center. Like the rest of the housing 2, the cross struts 40 are preferably stamped from a heat resistant metal sheet such a's stainless steel or aluminized steel. The cross struts 40 are anchored at their ends to the rims 16 of the sidewalls l2 and accordingly serve to maintain the sidewalls 12 in a fixed and determined position as the heater H is heated and cooled. Stamped into each cross strut 40 are retaining ears 44 which project laterally with respect to the housing 2 and are disposed outwardly from the strut posi-. tioning surface against which the bars 4 are positioned. The ears 44 are arranged in pairs with the ears 44 of each pair being generally aligned longitudinally of the housing 2, but projecting in opposite lateral directions. In other words, one car 44 of each pair projects toward one housing sidewall 12, while the other ear 44 of that pair projects toward the opposite sidewall 12. Thus, within adjacent pairs, there are oppositely directed ears which project into the space between that pair and hence toward one another. The space between opposed ears 44 in adjacent pairs is large enough to accommodate the back portion of one of the radiating bars 4 so that the bar 4 can be brought against the positioning surface of the cross strut 40. Hence, the ears 44 on the cross struts 40 serve to laterally position the radiating bars 4. The retaining ears 44 of the center cross strut 40, moreover, engage and interlock with projections on the back portions of the radiating bars 4 to prevent the radiating bars 4 from bowing outwardly at their centers as they are heated.

The positioning surface of each cross strut 40 extends behind the rear edges of rims 16 so that the cross struts 40 are in turn positioned by the rims 16 (FIG. 2). Moreover, the outwardly turned cars 44 in the outermost pairs thereof project into apertures in the sides of the rims so as to prevent the cross struts 44 from shifting longitudinally in the housing 2. Finally, the outermost ends of the strut 44 are turned forwardly behind the rims 16 to anchor the strut 44 firmly to the rims 16. This not only mounts the strut 44 within the housing 2, but also prevents the sidewalls 12 from bowing outwardly as the housing 2 is heated.

The radiating bars 4 occupy the portion of the housing 2 between the rims 16 on the sidewalls I2 and are captured between the positioning surfaces on the cross struts 40 and the cross flanges 30 on the end caps 24 when the end caps 24 are closed (FIGS. 1-3). However, when the end caps 24 are open, the radiating bars 4 are still held in the housing 2 by the retaining ears 44 on the center cross strut 44. The bars 4 are arranged side-by-side within the housing 2 and are prevented from moving inwardly by the struts 40 and outwardly by the cross flanges 30 on the end caps 24 and by the ears 44 on the center cross strut 44. The ears 44 further laterally position the bars with the housing and keep them from overlapping.

Each radiating bar 4 includes (FIGS. 5 and 6) a metal case 50 having a center or cross portion 52 which extends substantially the entire width of the bar 4 and forms the exposed portion thereof when the bar 4 is in the housing 2. The, outwardly presented surface of the center portion 52 is preferably covered with a coating having a high emissivity and the coated surface so formed constitutes the radiating or emissive surface of the bar 4. Also, it is desirable for the center portion 52 to have a slight amount of curvature in its transverse direction so that it possesses a concave configuration. At the side edges of the center portion 52, the case 50 doubles back upon itself, forming curved edge portions 54 and inwardly opening grooves 56 located behind the center portion 52. Finally, the case 50 turns rearwardly at the inner margins of the curved edge portions 54 to form rearwardly directed back or spacer flanges 58 which are spaced apart and parallel. The spacing between the two parallel back flanges 58 is such that the flanges 58 but not the curved edges 54 will fit between opposed retaining ears 44 in adjacent pairs of ears 44 on the cross struts 40 with only a slight amount of clearance (FIGS. 3). The flanges 58 are further deeper than the distance the retaining ears 44 are set away from the positioning surface on the cross struts 50 so that the rear margins of the flanges 58 will rest against the flat positioning surfaces on the cross struts 40, thus preventing the radiating bars 4 from moving further into the housing 2. Preferably, the metal of the case 50 is stainless steel.

The back flanges 58 turn outwardly adjacent the opposed retaining ears 44 of the center cross strut 40 only, forming outwardly flared tabs 60 which project behind the laterally directed ears 44 on the center cross strut 40. This prevents the bars 4 from bowing outwardly at their centers when they are heated and further prevents them from being withdrawn from the housing 2 when the end caps 24 are open. However, any bar 4 may be disengaged from its retaining ears 44 by sliding it longitudinally in the housing 2 until its outwardly flared tabs 60 clear the ears 44 of the center strut 40. This, of course, requires opening the end caps 24.

When the several radiating bars 4 are engaged with their respective retaining ears 44 on the center cross strut 40, the curved edges 54 of adjacent radiating bars 4 are presented close to one another and overlie and obscure the retaining ears 44 positioned between the adjacent bars 4. For all practical purposes, the concave portions 52 of the adjacent radiating bar cases 50 form a substantially continuous radiating surface across the open side of the housing 2.

Locked within the metal case 50 is a strip 68 of dielectric material, and that material is preferably sheet mica. The dielectric strip 68 lies against the back surface of the concave portion 52 and follows the contour thereof. Like the metal strip 50, the dielectric strip 68 turns inwardly at its side margins and in so doing follows the contour of the curved edges 54 on the metal strip 50. Thus, the inwardly opening grooves 56 exist within the dielectric strip 68 also. The inwardly turned portions of the dielectric strip 68 project inwardly slightly beyond the back flanges 58 on the metal case 50 so that the curved edges 54 are completely insulated from the interior of the bar 4 in an electrical sense.

Each radiating bar 4 further includes a heating element 70, which is preferably a sinuated wire. The convolutions of the sinuated element 78 traverse the interior of the bar 4, extending from one inwardly opening groove 56 to the other, and the lobes thereof are captured within the inwardly opening grooves 56, thus retaining the entire heating element 70 in place. Since the dielectric strip 68 lies against the back face of the center portion 52 and also against inwardly presented faces of the curved edges 54, the heating element 70 is completely isolated from the metal case 50 in an electrical sense. The heating element 70 need not be a wire, but may also be a stamping or some other suitable resistance heating element.

Spot welded or otherwise attached to the ends the sinuated heating element 70 are electrical connectors 72 which are likewise electrically isolated from the metal case 50 by the dielectric strip 60. The connectors 72 are also isolated from the end caps 24 by the dielectric insulating material 311.

The radiating bars are easily and quickly manufactured by converting flat stainless steel strip stock and flat dielectric material into the unique configuration of the bars 4 in a roll forming operation. in particular, flat dielectric material is laid against and centered on the wider flat stainless steel strip stock. The dielectric material at this point in the process should be capable of flexing quite severely without breaking. Impregnated mica paper meets these requirements. Once the dielectric strip is placed on the stainless steel strip stock the two are introduced into a rolling mill which rolls the two into a channel form with the dielectric strip being on the inside of the channel. The width of the channel form equals the width of the center portion 32 of the case 50 and consequently the dielectric strip also assumes the channel-shaped configuration also. Next, the sinuated wire element 70 is laid in the channel form against the dielectric strip thereof. Thereafter, the channel form with the sinuated heating element 70 therein is introduced into another rolling mill, and this rolling mill bends the side flanges of the channel form into the curved edges 54 and the back flanges 58. The second mill also imparts a concave configuration to the center portion of the channel form, thereby forming the center portion 52 of the case. As the flanges of the channel form are rolled into the curved edges 54 and the back flanges 58, the lobesof the heating element 70 are captured in the inwardly opening grooves 56 which I 68 is compressed snugly between the two. This assures maximum heat transfer from the element 70 to the center portion 52 of the case 50. Finally, a coating of high emissivity is painted on the case 50.

The connectors 72 of all of the radiating bars 4 are positioned 'adjacent to the end caps 24 where they are connected with bus bars 74 by means of short screws 76. The bus bars 72 are set inwardly from the back flanges 58 on the bars 48 and are isolated from the end walls 26 of the end caps 24 by the electrical insulating material 311 which lines those walls 26. The bus bars 74 in turn are carried by conductor bars 78 which extend along the back wall 114 of the housing 2 and lead to terminals mounted on the back wall 114. The conductor bars 78 are isolated from the back wall 14 by a sheet of dielectric material 82. More than one bus bar 78 may be used at each end, the exact number depending on the type of circuitry. indeed, the heater H, provides great flexibility as to the type of circuitry which may be employed and is .suitable for both single and multiphase alternating current.

The block 6 of insulating material is disposed behind the cross struts 48 and occupies the remainder of the housing 2 so as to retard the transfer of heat to the back side of the housing 2. The insulating material should further be a dielectric lPV" Supertemp Block which is marketed by Engle-Picher is suitable for the insulating material of the block 6.

While only three cross struts 40 have been illustrated spanning the housing 2, more may be employed, the number depending on the length of the housing 2. For example, in extended housings 2, it is desirable to have two cross struts 40 near the center of the housing instead of a single cross strut 40 at the center of the housing 2. The ears 44 on both of those cross struts 40 would engage tabs 60 on the bars 4 and thereby prevent the bars 4 from bowing outwardly at their centers. In any event, the important consideration is to have cross struts 48 near the ends of the housing 2 to prevent the bars from entering the insulative block 6 and at least one more cross strut 48 at or near the center of the housing to prevent the bars 4 from bowing outwardly. The centrally disposed cross struts 40 should of course engage tabs 60 on the bars 4, while the endmost cross struts 46 need not.

OPERATION The heater H is mounted by affixing the rearwardly projecting portions of its end caps 24 to a suitable supporting structure with the center portions 52 of the radiating bars 4 presented toward the area to be heated. In addition, the terminals 74 are connected across a suitable source of electrical energy.

In operation the connectors 72 of the individual radiating bars 4 are placed across the source of electrical energy so that current flows through the sinuated heating element 70. This, of course, elevates the temperature of the heating elements 78, and the heat so generated is transmitted through dielectric strips 60 to the metal cases 58. As a result the metal cases 50 become extremely hot and heat radiates from the center portions 52 thereof. More specifically, the electrical energy supplied the heating elements 70 of the bars 4 should be sufficient to raise the temperature of the bars to between 600F. and l400F. Consequently, the bars 4 radiate heat from the exposed surfaces of their center portions 52, and since the center portions 52 are covered with a coating having high emissivity, the emissivity of the radiating surface approaches that of a theoretical black body, making the heater H extremely efficient.

As the radiating bars 4 heat up to their operating temperature the centers thereof tend to move outwardly and the ends inwardly. In other words, the bars 68 tend to bow outwardly. The cross struts 40, however, restrain the bars 4 and prevent them from warping. In particular, the restraining ears 44 on the center cross strut 40 engage the tabs 60 on the bars 4 and prevent centers of the bars 4 from moving outwardly. The ends of the bars 4, on the other hand, bear against the cross struts 40 at the end of the housing and are thereby prevented from sinking into the insulative block 6. The restraining ears 44 on the end cross struts 40 further prevent the ends of the bars from shifting laterally and perhaps overlapping.

The concave configuration on the center portions 52 of the cases 50 for the bars 4 assures that those center portions 52 are as close as possible to their respective heating elements 70. This prevents the formation of blisters in the center portions 52 and adjacent hot spots" in the heating elements 70.

The radiating bars 4 are easily replaced merely by folding the end caps 24 outwardly (FIG. 2) to expose the ends of the radiating bars 4. Then the machine screws 76 opposite the ends ofthe bar 4 which is to be replaced are removed to disconnect the connectors 72 of that bar 4 from the bus bars 74. The bar 4 is then shifted longitudinally until its outwardly flared tabs 60 clear the laterally directed retaining ears 44 between which that bar 4 is positioned. Once free of the ears 44, the bar 4 is merely pulled outwardly and withdrawn from the housing 2. A new bar 4 is installed by the reversing the foregoing sequence. Consequently, the heater H is quite easy to service.

The heater H contains no ceramic or glass parts and no reflectors. On the contrary, high temperature steel and durable insulative materials such as mica are employed. As a result, the heater H can withstand repeated cycling and severe impacts without failure.

This invention is intended to cover all changes and modifications of the example of the invention herein chosen for purposes of the disclosure which do not constitute departures from the spirit and scope of the invention. I

What is claimed is:

l. A heating bar for a radiant heater, said bar comprising: a metal case having a cross portion on which an outwardly exposed heat emitting surface exists, the metal case being doubled back on itself at the sides of the cross portion to form inwardly opening grooves behind the cross portion, the doubled back portions merging into spacer flanges which project rearwardly away from the cross portion for engagement with a positioning surface by which the bar is positioned, the spacer flanges having outwardly projecting tabs thereon for engagement with means on a supporting structure for the bar; an electrically conductive heating element located behind the cross portion and extended into the inwardly opening grooves so as to be captured in the grooves; and a dielectric material between the heating element and the cross portion of the case.

2. A heating bar for an electric radiant heater; said bar comprising: a metal case having a cross portion with an outwardly exposed heat emitting surface on the front of the cross portion, the metal case being doubled back upon itself at the sides of the cross portion with the doubled back portions being formed integral with and being spaced rearwardly from the back face of the cross portion to form a pair of opposed grooves which open inwardly generally toward one another behind the cross portion, the doubled back portions at each side of the cross portion being spaced apart so that the grooves exist only along the sides of the cross portion, the cross portion being slightly curved in transverse cross-section with the curvature being such that its center is depressed with respect to the sides on the front face thereof; a dielectric material against the back face of the cross portion and being doubled back upon itself within the inwardly opening grooves of the metal case and lying against the doubled back portions of the case such that the inwardly opening grooves also exist in the dielectric material; and an electrical resistance-type heating element of a generally sinuated configuration extended behind the cross portion of the case for heating that cross portion, the lobes on one side of the heating element being captured in one of the inwardly opening grooves and the lobes on the other side being captured in the other inwardly opening groove, the heating element being separated from the metal case by the dielectric material which is interposed between the heating element and the doubled back and cross portions of the metal case to electrically isolate the heating element from the metal case.

3. A heating bar according to claim 2 wherein the doubled back portions of the case merge into spacer flanges which project rearwardly away from the heating element for engagement with a positioning surface by which the bar is positioned.

4. A heating bar according to claim 3 wherein the spacer flanges have outwardly projecting tabs thereon for engagement with means on a supporting structure for the bar.

5. A heating bar according to claim 2 wherein the doubled back portions include curved edges along which the doubled back portions merge into the cross portion, the curved edges forming the lateral extremeties of the heater bar.

6. A heating bar for an electric radiant heater, said bar comprising: a metal case having a cross portion with an outwardly exposed heat-emitting surface on the front of the cross portion, the metal case being doubled back upon itself at the sides of the cross portion with the doubled back portions being formed integral with and being spaced rearwardly from the back face of the cross portion to form a pair of opposed grooves which open inwardly generally toward one another behind the cross portion, the doubled back portions at each side of the cross portion being spaced apart so that the grooves exist only along the sides of the cross portion, the metal case further being turned rearwardly along the inner margins of the doubled back portions to form a pair of longitudinally extending spacer flanges; the spacer flanges being spaced apart and extending substantially the entire length of the metal case; securing means on the spacer flanges for securing the heating bar to a supporting structure; an electrical resistancetype heating element located behind the cross portion, the heating element being of a substantially sinuated configuration with the lobes on one side thereof being captured in one of the grooves and the lobes in the other side being captured in the other groove, the heating element being substantially free to flex rearwardly between the doubled back portions; and a dielectric material against the inwardly presented faces of the doubled back portions so that the inwardly opening grooves also exist in the dielectric material, the dielectric material being interposed between the heating element and the metal case to electrically isolate the case from the element.

7. A heating bar according to claim 6 wherein the cross portion of the case is curved inwardly toward the heating element located behind it to insure high heat transfer through the dielectric material.

8. A heating bar according to claim 6 wherein the dielectric material is a thin strip which likewise doubles back upon itself at the sides of the case so that the inwardly opening grooves also exist in the dielectric maon the spacer flanges. 

1. A heating bar for a radiant heater, said bar comprising: a metal case having a cross portion on which an outwardly exposed heat emitting surface exists, the metal case being doubled back on itself at the sides of the cross portion to form inwardly opening grooves behind the cross portion, the doubled back portions merging into spacer flanges which project rearwardly away from the cross portion for engagement with a positioning surface by which the bar is positioned, the spacer flanges having outwardly projecting tabs thereon for engagement with means on a supporting structure for the bar; an electrically conductive heating element located behind the cross portion and extended into the inwardly opening grooves so as to be captured in the grooves; and a dielectric material between the heating element and the cross portion of the case.
 2. A heating bar for an electric radiant heater; said bar comprising: a metal case having a cross portion with an outwardly exposed heat emitting surface on the front of the cross portion, the metal case being doubled back upon itself at the sides of the cross portion with the doubled back portions being formed integral with and being spaced rearwardly from the back face of the cross portion to form a pair of opposed grooves which open inwardly generally toward one another behind the cross portion, the doubled back portions at each side of the cross portion being spaced apart so that the grooves exist only along the sides of the cross portion, the cross portion being slightly curved in transverse cross-section with the curvature being such that its center is depressed with respect to the sides on the front face thereof; a dielectric material against the back face of the cross portion and being doubled back upon itself within the inwardly opening grooves of the metal case and lying against the doubled back portions of the case such that the inwardly opening grooves also exist in the dielectric material; and an electrical resistance-type heating element of a generally sinuated configuration extended behind the cross portion of the case for heating that cross portion, the lobes on one side of the heating element being captured in one of the inwardly opening grooves and the lobes on the other side being captured in the other inwardly opening groove, the heating element being separated from the metal case by the dielectric material which is interposed between the heating element and the doubled back and cross portions of the metal case to electrically isolate the heating element from the metal case.
 3. A heating bar according to claim 2 wherein the doubled back portions of the case merge into spacer flanges which project rearwardly away from the heating element for engagement with a positioning surface by which the bar is positioned.
 4. A heating bar according to claim 3 wherein the spacer flanges have outwardly projecting tabs thereon for engagement with means on a supporting structure for the bar.
 5. A heating bar according to claim 2 wherein the doubled back portions include curved edges along which the doubled back portions merge into the cross portion, the curved edges forming the lateral extremeties of the heater bar.
 6. A heating bar for an electric radiant heater, said bar comprising: a metal case having a cross portion with an outwardly exposed heat-emitting surface on the front of the cross portion, the metal case being doubled back upon itself at the sides of the cross portion with the doubled back portions being formed integral with and being spaced rearwardly from the back face of the cross portion to form a pair of opposed grooves which open inwardly generally toward one another behind the cross portion, the doubled back portions at each side of the cross portion being spaced apart so that the grooves exist only along the sides of the cross portion, the metal case further being turned rearwardly along the inner margins of the doubled back portions to form a pair of longitudinally extending spacer flanges; the spacer flanges being spaced apart and extending substantially the entire length of the metal case; securing means on the spacer flanges for securing the heating bar to a supporting structure; an electrical resistance-type heating element located behind the cross portion, the heating element being of a substantially sinuated configuration with the lobes on one side thereof being captured in one of the grooves and the lobes in the other side being captured in the other groove, the heating element being substantially free to flex rearwardly between the doubled back portions; and a dielectric material against the inwardly presented faces of the doubled back portions so that the inwardly opening grooves also exist in the dielectric material, the dielectric material being interposed between the heating element and the metal case to electrically isolate the case from the element.
 7. A heating bar according to claim 6 wherein the cross portion of the case is curved inwardly toward the heating element located behind it to insure high heat transfer through the dielectric material.
 8. A heating bar according to claim 6 wherein the dielectric material is a thin strip which likewise doubles back upon itself at the sides of the case so that the inwardly opening grooves also exist in the dielectric material.
 9. A heating bar according to claim 6 wherein the spacer flanges are parallel.
 10. A heating bar according to claim 6 wherein the spacer flanges rearwardly terminate at margins which are equally spaced from the cross portion and are adapted to engage a positioning surface to correctly position the heating bar.
 11. A heating bar according to claim 6 wherein the securing means is arranged on the spacer flanges to prevent the midportion of the heating bar from bowing forwardly.
 12. A heating portion according to claim 11 wherein the securing means comprise outwardly directed tabs on the spacer flanges. 